The present invention relates generally to continuous forming apparatus and methods for forming foam materials into three-dimensional shapes. Generally, the production of three-dimensional products made from a foam material requires a mold that can both define the three-dimensional shape and contain any pressure exerted by the foam material until the product is rigid enough to be removed from the mold.
To accomplish these requirements, currently available production apparatus for continuous production include endless flexible mold belts and chain-mounted rigid mold sections. Endless flexible mold belts that are used to form 3-D products on a continuous basis may be done by arranging one or more flat belts edge to edge so as to form a cavity, or by using two thicker belts, arranged face to face, with a cross sectional shape extending into one or both of the belt faces. As used herein, the term “flat” means relatively flat so that a flat surface may be rough and include any type of surface finish.
The belts may be incorporated into a motorized forming apparatus similar to a conveyor belt machine. The belts are typically fabric-reinforced, and may be faced with an elastomeric, contoured face so as to allow the molding of deeper features and to provide the mold belt with sufficient flexibility to bend around the pulleys of the motorized forming apparatus. An extruder or other delivery system may be used to deliver material into one end of a forming apparatus where it is held and conveyed within a mold belt cavity until the material is sufficiently cured or cooled to maintain its shape after being expelled from the apparatus. These currently available belt-driven continuous forming apparatus are typically used to produce small cross sectional area products.
The production of parts with larger cross sections or deeper surface detail typically requires the use of a machine that utilizes chain-mounted rigid mold sections. For example, foam parts with surface detail like imitation wood beams are sometimes produced on a continuous basis using these continuous forming apparatus. However, these machines are extremely expensive and adjacent mold sections must fit together precisely to prevent material from oozing and binding between mold sections.
Large foam buns are continuously cast in square forming machines that are comprised of table-top conveyors using thin flat plates attached to chains. Multiple belts of flat plates are combined to make a continuous square cavity to support and mold the foam product. A wax paper or plastic film is used to prevent the foaming material from sticking to and leaking between the plates. The buns are then slit to make mattresses and the like.
While mold belts may define the desired three-dimensional product shape, they must be driven in the direction of production, and supported so as to contain the pressure of the foaming material without deforming. Typically, these belts are driven by a motorized pulley and supported by either slider-beds or by support rollers in much the same way as a conventional conveyor belt. Slider-bed supported systems must overcome the pressure-induced friction between the back of the belt and the slider-bed. The wider the product and longer the forming apparatus, the greater the friction that the drive mechanism must overcome, which limits the practical size of a slider-bed supported forming apparatus for foam materials.
Roller-supported mold belts minimize belt-to-bed friction, but the belts are unsupported in the spans' between adjacent rollers, allowing the belt to deflect outward. The roller-bed supported belts virtually eliminate the friction associated with slider-beds, but the foaming pressure on the belt is not supported between individual rollers allowing the belts to intermittently gap open as they travel.
The friction problem of the slider-bed may be mitigated by using air film lubrication. However, the foaming pressure is not constant along the length of the machine, especially for thermoset foams. Thus, air film lubrication requires the regulation of air pressure to discrete pressure zones along the machine's length. Additionally, air film lubrication is limited to smaller parts with low foaming pressures in order to avoid using excessively high-pressure air.
Accordingly, a need exists for continuous forming apparatus that fully support high foaming pressures while the foam material cools and cures. Furthermore, a need exists for continuous forming apparatus that experiences minimal frictional forces so that the continuous forming apparatus is able to mold wider foam products without sacrificing the dimensional accuracy, surface detail, and desired cross section of the foam product.